The long-range objectives of this project are to establish the role of the cytokines IL-12 and IL-23 and their signaling pathways in the generation and maintenance of human memory CD4+ T cells and to determine important domains and factors involved in IL-12Rbeta1, IL-12Rbeta2, and IL-23R cell surface expression and function. This research proposal stems from the surprising observation of a decrease in both number and function of effector memory CD4+ T cells (CD45ROhigh CCR7 low) cells with a high capacity for IFN-gamma production) in a patient with a genetic deficiency of IL-12Rbeta1 involving the cytoplasmic tail. CD4+ T cells from this patient and his heterozygous family members also showed a marked decrease in not only surface expression of IL-12Rbeta1 but also IL-12Rbeta2. These additional findings suggest a model whereby the mutant IL-12Rbeta1 protein acts as a dominant negative, and interferes with a normal intracellular event in which the two IL-12 receptor chains interact prior their expression at the cell surface expression. The two major hypotheses of the proposed research are that: 1) IL-12 and IL-23 are important for protecting memory CD4 T cells from apoptosis, and are required for the conversion of central memory (CD45ROhighCCRhigh CD4+ T cells, lacking the capacity for IFN-\gamma production, into effector memory (CD45ROhighCCR7lowcells), with high levels of IFN-gamma production; and 2) that the cytoplasmic domain of IL-12R?1 is necessary for optimal CD4+ T cell surface expression and function of the specific IL- 12 IL-12Rbeta1/IL-12Rbeta2) and IL-23 (IL-12Rbeta1/IL-23R) receptors. Our specific aims are to: 1) Determine the role of IL-12 and IL-23 in the generation and survival of human CD4+ Tem cells; 2) Determine the molecular domains and factors necessary for IL-12Rbeta1 cell surface expression and function; and 3) Determine the mechanism(s) for decreased surface IL-12 receptor expression in a patient with homozygous IL-12Rbeta1 deficiency due to a cytoplasmic tail mutation and in his heterozygous relatives. The proposed work will provide substantial new insights into the regulation of Th1 responses and CD4+ memory T cell generation by IL-12 and IL-23, and may indicate new approaches for therapeutic enhancement of such responses, such as for infections or cancer. The proposed training program is in a dynamic research setting with extensive intellectual and technical support. Thus, by pursuing this K08 project, the candidate will acquire the skills to become an independent investigator in a line of inquiry relevant to immunology and hematology/oncology.